Ghasts are undead souls of people that starved to death in Mort Myre swamp. When first encountered, they are almost transparent, have no combat level, and try to turn food into useless rotten food. If a player has a container of food, such as a hamper or a sack of onions, and the ghast is successful, the container and its contents will become rotten. Food that cannot be directly eaten, such as watermelons, will still be turned into rotten food. They cannot rot raw food that must be cooked before being eaten, however, with the exception of raw potatoes. If a player has no food, they deal damage instead.
If a ghast attacks a player with a charged pouch (or a player uses a charged pouch on a ghast), the ghast becomes visible and one charge is consumed. In this way, a charged pouch protects a player's food from being rotten. Visibility renders the ghast vulnerable to attack.
The regular ghasts encountered in Mort Myre are level 50, and the higher level ghasts are encountered during Temple Trekking. Killing any level of ghast rewards the player with 30 Prayer experience.
Although not difficult, it is considered by some to be rather tedious to summon ghasts for combat training. They do drop lots of herbs, much more so than hobgoblins. The material drops are rather petty. You do, however, gain reasonable Prayer experience as well as combat experience for killing them. The salve amulet gives combat bonuses on ghasts.
The best place to hunt them would be just west of the Nature Grotto from the Nature Spirit quest. This allows you to keep refreshing your Prayer points without using valuable prayer potions. The silver sickle does not have to actually equipped to gain its benefits, it just has to be in your inventory. However, you must also have a filled druid pouch in your inventory to prevent your food from being rotted. A player can use whichever weapon they choose for combat, not having to use the sickle. Fully charge your Prayer points, go west of the grotto (where the ghasts are) and cast Bloom with the sickle next to the rotten logs. Try and do it between as many logs, branches, and bushes as possible, and you will often get several blossomed items to put in the druid pouch. Do this over and over until you are out of Prayer points. Now "use" the filled pouch on the ghostly ghasts - do not wait for them to attack you. Often they will just float around, or the pouch will activate itself, allowing the solid ghast to float out over the water where it cannot be attacked. The drops will more often than not fall under the rotten logs, so search the ground carefully after defeating the ghast.
Ghasts are in fact humans who have been transformed due to a lack of food, as proven during the Temple Trekking minigame. This explains why ghasts attempt to steal and consume food from players. When one is in the Morytanian environment and does not eat enough, the following will occur:
At first the human looks hungry, but normal.
The hair colour will begin to fade. The victim's skin will turn to a purple-adjacent colour.
The hair will become completely grey and might fall out or grow even more, the cheeks and nose begin to "slump" and the skin turns to a more brown colour. The white of the eye will become slightly yellow.
If the person still hasn't eaten, their skin turns blue-grey and completely loses elasticity. The white of the eye is now completely yellow.
Finally, the victim turns into a ghast, at which point they can no longer be cured.
If a ghast dies above water, there will be no drop at all. This also applies to the Vyrewatch in Meiyerditch near the boat.
If you finished Deadliest Catch you have access to a bank deposit box somewhat north-west from the grotto where you can bank your herbs and other drops.
Since their graphical update on 17 August 2011 the ghasts now have same moving, idle and death animations as the aberrant spectres.
If attacked by a Ghast while using a Home teleport, the animation will be interrupted, although the teleport will not, even if the Ghast does damage to you, only when it is transparent.
When a ghast dies, its spirit resembles the way it used to look before their graphical update.
With the update to Temple Trekking on 17 August 2011, the ghasts in the events no longer gave Prayer experience. This glitch was fixed on 7 February 2012.
There is currently a glitch where, if you teleport to the Lunar Isle using the lodestone network, are attacked during the animation, arrive on Lunar Isle, log out, and log back in, there will be a ghast. It does not attack you or follow you, and using a druid pouch on it will have no effect; it can only be examined.